<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  
  <script>
    const fileName = 'example.png';

    const res = fileName.slice(fileName.indexOf('.'))
    console.log(res)
  </script>
</body>
</html>